tivities they appear to drink regularly, the prolonged survival without water in the
laboratory being substantially the result of their inactivity, and the lack of necessity
to travel far in search of food . Their relatively low rate of water loss must allow
them to cover considerable distances and survive the difficult 12 to 24 h period
between drinks. This may be of considerable importance, especially when it is remembered that during the hottest time of the year in such arid areas even a man
is only expected to survive for about a day without water (ADOLPH, 1947). Their
tolerance to dessication has not been reported. The distance which these small birds
normally cover in search of food and water is unknown, but TUCKER (1968) has
measured the rates of water loss of budgerygahs flying at different ambient temperatures. When flying at 35 km an hour in a wind tunnel at 20
0
the net water
loss (water loss minus gain of metabolic water) of a budgerygah is equivalent to
1.1% of its body weight in an hour, which, if it can withstand a total water loss
amounting to 15% of its weight, would allow the bird to fly for 14 h and travel
490 km. At 30
0 the rate of water loss was about 25% greater. At 36
0 to 37
0 the
water loss was 3 times as great as at 20
0
, and the birds could only fly for about
20 min as they became overheated. These very elegant experiments suggest that
the budgerygah in its native habitat can travel considerable distances to feeding
and watering places each day, but preferably not during the hottest times of the
day. In the middle of the day budgerygahs are known to rest in the shady branches
of trees, moving about mainly in the morning and late afternoon.
In the laboratory both budgerygahs and zebra finches can be persuaded to drink
saline solutions. The latter species can maintain their body weight when drinking
0.2 M sodium chloride solutions while the budgies can tolerate 0.4 M solutions.
In natural conditions it is unlikely that these birds resort to saline drinking, but
the y could do so in peculiar circumstances.
While physiological adjustments play an important role in the day-to-day life
of budgerygahs and zebra finches, the most vital adaptation ensuring the survival
of the species in arid regions is their breeding behaviour. Day length plays a predominant role in the regulation of reproduction of birds of many species, but other
factors including rainfall also influence this (see FARNER and FOLLETT, 1966). Certain African and Australian birds , including the budgerygah and zebra finch , breed
irr egularly, usuall y only doing so in response to rain or factors such as food that
are associated with rain (see MARSHALL, 1961). The exact nature of the environmental stimulus is unknown but the hypothalamic-neuroendocrine systems is activated (OKSCHE et al., 1963) and this sets in motion the rest of the endocrine and
metabolic machinery associated with reproduction. Reproduction is associated
with an increased need of food and water for egg production and feeding the young.
For birds living in areas where rain and adequate food supplies are unpredictable,
such a breeding pattern would be an advantage. Indeed the survival of the species
in such areas is difficult to imagine if regular breeding, irrespective of the often
adverse conditions, were to occur.
While osmotic conditions and the endocrine system interact to ensure successful reproduction in the budgerygah and zebra finch, the evidence for a role of hormones in the osmoregulation of these birds is largely circumstantial. The anatomy
of the hypothalamo-hypophysial neurosecretory system in these two species has
been investigated (OKSCHE et al., 1963; KOBAYASHI et aI., 1961). Vasotocin has
133
laboratory being substantially the result of their inactivity, and the lack of necessity
to travel far in search of food . Their relatively low rate of water loss must allow
them to cover considerable distances and survive the difficult 12 to 24 h period
between drinks. This may be of considerable importance, especially when it is remembered that during the hottest time of the year in such arid areas even a man
is only expected to survive for about a day without water (ADOLPH, 1947). Their
tolerance to dessication has not been reported. The distance which these small birds
normally cover in search of food and water is unknown, but TUCKER (1968) has
measured the rates of water loss of budgerygahs flying at different ambient temperatures. When flying at 35 km an hour in a wind tunnel at 20
0
the net water
loss (water loss minus gain of metabolic water) of a budgerygah is equivalent to
1.1% of its body weight in an hour, which, if it can withstand a total water loss
amounting to 15% of its weight, would allow the bird to fly for 14 h and travel
490 km. At 30
0 the rate of water loss was about 25% greater. At 36
0 to 37
0 the
water loss was 3 times as great as at 20
0
, and the birds could only fly for about
20 min as they became overheated. These very elegant experiments suggest that
the budgerygah in its native habitat can travel considerable distances to feeding
and watering places each day, but preferably not during the hottest times of the
day. In the middle of the day budgerygahs are known to rest in the shady branches
of trees, moving about mainly in the morning and late afternoon.
In the laboratory both budgerygahs and zebra finches can be persuaded to drink
saline solutions. The latter species can maintain their body weight when drinking
0.2 M sodium chloride solutions while the budgies can tolerate 0.4 M solutions.
In natural conditions it is unlikely that these birds resort to saline drinking, but
the y could do so in peculiar circumstances.
While physiological adjustments play an important role in the day-to-day life
of budgerygahs and zebra finches, the most vital adaptation ensuring the survival
of the species in arid regions is their breeding behaviour. Day length plays a predominant role in the regulation of reproduction of birds of many species, but other
factors including rainfall also influence this (see FARNER and FOLLETT, 1966). Certain African and Australian birds , including the budgerygah and zebra finch , breed
irr egularly, usuall y only doing so in response to rain or factors such as food that
are associated with rain (see MARSHALL, 1961). The exact nature of the environmental stimulus is unknown but the hypothalamic-neuroendocrine systems is activated (OKSCHE et al., 1963) and this sets in motion the rest of the endocrine and
metabolic machinery associated with reproduction. Reproduction is associated
with an increased need of food and water for egg production and feeding the young.
For birds living in areas where rain and adequate food supplies are unpredictable,
such a breeding pattern would be an advantage. Indeed the survival of the species
in such areas is difficult to imagine if regular breeding, irrespective of the often
adverse conditions, were to occur.
While osmotic conditions and the endocrine system interact to ensure successful reproduction in the budgerygah and zebra finch, the evidence for a role of hormones in the osmoregulation of these birds is largely circumstantial. The anatomy
of the hypothalamo-hypophysial neurosecretory system in these two species has
been investigated (OKSCHE et al., 1963; KOBAYASHI et aI., 1961). Vasotocin has
133